I replace mine when it is "skipping" and I need to go over it more than once. Of course, when you run over a pin that is hiding on your cutting board ( :thumbdown: :thumbdown: ) that does not help.
I did purchase one of those sharpeners at JoAnns - the small rotary one - in hopes of when I AM a dummy and manage to run over a pin I could reclaim the blade a bit. It doesn not work badly but never as well as a new blade.
I just bought a stack of new blades from
http://jhittlesewing.funoverload.com...new_items.html
They work great and a lot less expensive than retail. I will change them more frequently now!!